Polymeric Dispersants, Dispersions, Processes for Preparing Dispersions and the Use of Polymeric Dispersants

ABSTRACT

A polymeric dispersant obtained or obtainable by copolymerising a monomer composition comprising at least the components: i) benzyl (meth)acrylate; ii) propylene glycol (meth)acrylate; wherein the weight ratio of component i) to component ii) is greater than 10:1.

TECHNICAL FIELD

This invention relates to polymeric dispersants, it further relates todispersions comprising the polymeric dispersant, a particulate solid(especially a pigment) and a liquid medium. These dispersions areespecially suitable for preparing ink jet printing inks. The presentinvention also relates to a process for preparing said dispersions andto the use of the polymeric dispersants for preparing ink jet printinginks. The dispersants described in the present invention are especiallysuited to the stable dispersion of yellow pigments (e.g. C.I. PigmentYellow 74 and C.I. Pigment Yellow 155).

BACKGROUND

Inks are often of one of two types, depending on the type of colorantused. Dye-based inks often comprise a dye dissolved in a liquid vehicle.Pigment inks comprise a pigment dispersed in a particulate form in aliquid vehicle. Pigment inks tend to have better ozone-fastness andlight-fastness than dye-based inks. However, because the pigment is inthe form of fine particles there is a tendency for the particles toagglomerate or flocculate whilst the ink is being stored and/or whilstthe ink is being used (e.g. printed). Such agglomeration or flocculationbefore the ink has been printed onto a substrate is highly undesirable,particularly in ink jet printing inks where the printer nozzles are verysmall and are susceptible to blockage by any oversized particulatematter. Thus, in the ink jet field a great deal of effort has been spentattempting to provide sub micron sized pigment dispersions and increasethe colloidal stability of these pigment dispersions.

It is also desirable to provide pigment inks which offer high opticaldensity (OD), especially when printed onto plain paper.

Pigment dispersions are often colloidally stabilised by means of adispersant.

It is desirable that a dispersant is effective in the dispersion orcomminution process. Quicker comminution (e.g. milling) to submicronparticles sizes saves substantial energy and it may also result in lesspigment particles having a particles size markedly smaller than thetarget size. Particles much below the target size are often referred toas fines.

Pigment based inks when printed onto a substrate often produce finalimages that are not firmly secured to the substrate surface. Prints frompigment based inks often exhibit poor rub fastness, water-fastness orhighlighter smear fastness.

In our own studies C.I. Pigment Yellows and especially C.I. PigmentYellow 155 and C.I. Pigment Yellow 74 have proved to be particularlydifficult to disperse to a suitably small particle size for preparingink jet printing inks. In our studies the milling times required for thepreparation of C.I. Pigment Yellow 74 dispersions with an averageparticle size of around 100 nm can often be twice as long as those forcyan, magenta and black pigments at the same average particle size. Thisrepresents a substantial cost in providing the required milling energy.

It is known that dispersions of C.I. Pigment Yellow 74 pigments tend tohave relatively poor colloidal stability resulting in flocculation,particle size growth and sedimentation whilst being stored and/or whilstin the printer. Such is recognised by for example PCT patent publicationWO 2010/068776.

In our studies we have seen that the colloidal instability of thedispersions are more pronounced at elevated storage temperatures, overlonger storage times and in liquid vehicles which contain smallerproportions of water relative to water-miscible organic liquids.

The above problems limit the performance and adoption of C.I. PigmentYellows in ink jet printing inks.

Commercially, there still remains a need for dispersants which can beused to prepare pigment inks (especially inks containing the pigmentsC.I. Pigment Yellow 74 and 155) which solve, at least in part, one ormore of the abovementioned problems.

DETAILED DESCRIPTION

According to a first aspect of the present invention there is provided apolymeric dispersant obtained or obtainable by copolymerising a monomercomposition comprising at least the components:

i) benzyl (meth)acrylate;ii) propylene glycol (meth)acrylate;wherein the weight ratio of component i) to component ii) is greaterthan 10:1.

DEFINITIONS

Unless stated to the contrary, in the present patent the words “a” and“an” are meant to include the possibility of using one or more of thatitem.

Component i) Benzyl (Meth)Acrylate

Benzyl (meth)acrylate has the structure:

wherein R is H or more preferably methyl.

Component i) may comprise benzyl methacrylate, benzyl acrylate or amixture thereof. Preferably, component i) comprises benzyl methacrylate.In a more preferred case component i) is benzyl methacrylate.

Preferably, component i) is present in at least 40, more preferably atleast 50, even more preferably at least 55, especially at least 60 andeven more especially at least 65 parts and most especially at least 70parts by weight.

Preferably component i) is present at no more than 95, more preferablyno more than 90 and especially no more than 85 parts by weight.

Especially preferred ranges for the amounts of component i) are 40 to95, 50 to 90, 60 to 90, 65 to 90 and 70 to 90 parts by weight.Preferably, these parts represent the amounts of benzyl methacrylate.

Component ii) Propylene Glycol (Meth)Acrylate

Propylene glycol (meth)acrylate exists in a number of isomeric forms allof which are covered by the descriptions and claims herein.

2-hydroxypropyl (meth)acrylate and propylene glycol mono(meth)acrylateare also names commonly attributed to the same monomer.

Preferably, propylene glycol (meth)acrylate comprises, more preferablyis one or both of the isomeric structures indicated directly below:

wherein R is H or more preferably CH₃.

Materials for component ii) often tend to be mixtures of these twopropylene glycol (meth)acrylate isomers.

Propylene glycol (meth)acrylate preferably comprises or is the isomericstructure:

wherein R is H or more preferably CH₃. Preferably, this isomericstructure accounts for more than 10%, more preferably more than 25% andespecially more than 50% by weight of all the propylene glycol(meth)acrylate isomers present.

Component ii) may comprise propylene glycol methacrylate, propyleneglycol acrylate or a mixture thereof. Preferably, component ii)comprises propylene glycol methacrylate. In a more preferred casecomponent ii) is propylene glycol methacrylate.

Preferably, component ii) is present at no more than 9, more preferablyno more than 8, even more preferably no more than 7, especially no more6.5 and most especially no more than 6 parts by weight.

Preferably component ii) is present in at least 0.1, more preferably atleast 1, even more preferably at least 2, especially at least 3 and mostespecially at least 4 parts by weight.

Especially preferred ranges for the amounts of component ii) are 0.1 to9, 1 to 8, 2 to 8, 3 to 8 and 4 to 7 parts by weight.

Preferably, these parts represent the amounts of propylene glycolmethacrylate (including all the abovementioned isomeric forms).

Optional Components in the Monomer Composition

The monomer composition may additionally comprise one or more furthermonomers.

The further monomers are preferably ethylenically unsaturated monomersother than those already mentioned in components i) and ii).

The further monomers may be one or more hydrophilic or hydrophobicmonomers. Combinations of both further hydrophilic and hydrophobicmonomers may be present in the monomer composition.

iii) Hydrophilic Further Monomers

Preferred hydrophilic further monomers have one or more hydrophilicgroups. The hydrophilic groups may be non-ionic or more preferablyionic.

Non-ionic hydrophilic groups include polyethyleneoxy (ended in hydroxyor alkyl chains). Examples of which include polyethyleneglycol(meth)acrylates. Preferably, if such monomers are present they accountfor less than 10 part, more preferably less than 5 parts, especiallyless than 2 parts by weight, more especially no monomer used in thepreparation of the dispersant has polyethyleneoxy groups. Preferredpolymeric dispersants do not have polyethyleneoxy groups because we haveseen that these groups tend to reduce the final optical density of theprinted images.

Preferably, the monomer composition further comprises iii) one or moreethylenically unsaturated hydrophilic monomers each having one or moreionic groups.

The ionic groups may be anionic or cationic. Examples of anionic groupsinclude phosphonic acid, phosphoric acid, sulfonic acid and especiallycarboxylic acid groups. These may be in the free acid, salt form or acombination thereof. Suitable salt forms include those with the alkalimetal ions (especially sodium potassium and lithium), ammonium,substituted ammonium and alkanolammonium ions.

Preferably, the hydrophilic further monomers have a calculated Log Pvalue of less than 1. Preferably the calculated Log P value is from lessthan 1 to −6, more preferably from less than 1 to −3.

A review by Mannhold, R. and Dross, K. (Quant. Struct-Act. Relat. 15,403-409, 1996) describes 14 methods for calculating Log P values ofcompounds and especially drugs. From this review we prefer the“fragmental methods” and especially the fragmental method implemented byACD labs software. The calculated Log P of a monomer may be calculatedusing commercially available computer software, for example using theLog P DB software version 7.04 or a later version of such software(which is available from Advanced Chemistry Development Inc (ACD labs)).Any ionic or ionisable groups are calculated in their neutral(unionised) form. A lower log P value corresponds to a more hydrophilicmonomer.

Preferred hydrophilic further monomers have a solubility in water at 25°C. of at least 5% by weight, more preferably at least 10% by weight. Forthe purposes of determining the solubility the monomer is 100%neutralised with potassium hydroxide in the case or anionic groups andnitric acid in the case of cationic groups.

Preferred hydrophilic further monomers include beta carboxylethylacrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, morepreferably acrylic acid and especially methacrylic acid. Preferably,component iii) in the monomer composition is or comprises methacrylicacid.

Preferably, the monomer composition additionally comprises a furtherhydrophilic monomer in an amount of at least 0.1, more preferably atleast 1, even more preferably at least 2, especially at least 4, moreespecially at least 6 and even more especially at least 8 parts and mostespecially at least 10 parts by weight.

Preferably, the monomer composition comprises no more than 35, morepreferably no more than 30, even more preferably no more than 25 andespecially no more than 20 parts and most especially no more than 15parts by weight of hydrophilic further monomer.

Preferably, the monomer composition comprises from 0.1 to 35, morepreferably from 1 to 35, even more preferably from 4 to 30 andespecially from 6 to 25, even more especially from 10 to 25 and mostespecially from 10 to 15 parts by weight of further hydrophilicmonomers. Preferably, these are the amounts of methacrylic acid presentin the monomer composition.

iv) Hydrophobic Further Monomers

Preferred hydrophobic ethylenically unsaturated monomers are thosehaving one or more hydrophobic groups. Preferred hydrophobic groupsinclude alkyl, aryl, siloxane or fluoroalkyl groups.

Preferably, the further hydrophobic monomers have no hydrophilic groupswhether ionic or non-ionic. For example, they are preferably free of anyionic or polyethyleneoxy groups as mentioned previously.

Preferably, the hydrophobic ethylenically unsaturated monomers have acalculated Log P value of at least 1, more preferably from 1 to 6,especially from 1 to 4.

Preferred hydrophobic further monomers have a solubility in water at 25°C. of less than 5% by weight, more preferably less than 2% by weight.

Preferred hydrophobic ethylenically unsaturated monomers are styrenicmonomers (e.g. styrene, alpha methyl styrene), aromatic (meth)acrylates(other than benzyl acrylate and benzyl methacrylate), C₁₋₃₀-hydrocarbyl(meth)acrylates, butadiene, isoprene, (meth)acrylates containingpoly(C₃₋₄alkylene oxide groups, (meth)acrylates containing alkylsiloxaneor fluorinated alkyl groups and vinyl naphthalene.

Preferably, the monomer composition comprises no more than 50 parts,more preferably no more than 30 parts, even more preferably no more than10 parts, especially no more than 2 parts and most especially 0 parts ofthese further hydrophobic monomers.

Preferably the monomer composition comprises no more than 10 parts, morepreferably no more than 5 parts, especially no more than 2 parts andmost especially 0 parts by weight of macromonomers by weight. Examplesof macromonomers which are preferably absent include polyalkyleneoxy(meth) acrylates, styrenic macromonomers and polysiloxy containingmacromonomers.

Preferred Monomer Compositions

In view of the foregoing a preferred monomer composition comprises:

-   i) 40 to 95 parts, more preferably 60 to 90, especially 70 to 90    parts of benzyl methacrylate;-   ii) 0.1 to 9 parts, more preferably 2 to 8, especially 4 to 7 parts    of propylene glycol methacrylate;-   iii) 1 to 35 parts, more preferably 6 to 25, especially from 10 to    15 parts of methacrylic acid;-   iv) 0 to 50 parts, more preferably 0 to 30 parts, especially 0 to 10    parts of further hydrophobic monomers;    wherein all the parts are by weight and the ratio of component i)    to ii) is greater than 10:1.

In all cases the sum of the parts of all the monomers in the monomercomposition preferably adds up to 100 parts by weight. In such a casethe number of parts of the monomer components equates to percentages byweight relative to the entire monomer composition.

Ratio of Component i) to Component ii)

Preferably, the weight ratio of component i) to component ii) is from11:1 to 100:1, more preferably from 11:1 to 50:1, especially from 11:1to 25:1, more especially from 11:1 to 20:1 and most especially from 11:1to 16:1.

The inventors were surprised by the present invention, in that:

-   i) propylene glycol (meth)acrylate does not have a sterically    stabilising polymeric chain as found in polypropylene glycol    (meth)acrylate and so it was unexpected to find that it provided    polymeric dispersants offering dispersions with such good colloidal    stability.-   ii) dispersions having good colloidal stability are achieved even    with difficult pigments such as C.I. Pigment Yellow 155 and 74.-   iii) the amounts of propylene glycol (meth)acrylate in the polymeric    dispersant required to gain sufficiently beneficial improvements in    colloidal stability are unexpectedly low.-   iv) the milling times required to prepare dispersions of C.I Yellow    155 and 74 are unexpectedly short.

Polymeric Dispersant Characteristics

Preferably, the polymeric dispersant has a weight averaged molecularweight of less than 100,000, more preferably less than 50,000 andespecially less than 40,000 g per mole.

Preferably, the polymeric dispersant has a weight averaged molecularweight of at least 1,000, more preferably at least 5,000 and especiallyat least 10,000 g per mole.

The molecular weight is preferably measured by gel permeationchromatography (GPC). The molecular weight standards employed arepreferably polyethylene glycol or more preferably polystyrene. Theeluent used for GPC is preferably dimethyl formamide (DMF),tetrahydrofuran (THF) or acetone. Of these DMF is preferred.

The polymeric dispersant preferably has an acid value of from 0.5 to 4mmoles, more preferably 0.5 to 3 mmoles, especially from 1 to 3 mmoles,even more especially from 1.0 to 2.5 mmoles and most especially from 1.2to 2 mmoles per g of dispersant.

The acid value may be calculated from the monomer composition.Alternatively the acid value may be experimentally determined bytitration.

Preferably, the only acid groups in the polymeric dispersant whichprovide the abovementioned acid value are phosphonic and/or carboxylicacid, more preferably carboxylic acid groups.

The polymeric dispersant may be branched or partially cross-linked butis preferably linear (prior to the optional cross-linking mentionedbelow).

The polymeric dispersant may have a block, graft or more preferably arandom structure with regard to the distribution of the monomer repeatunits.

The polymeric dispersant is preferably soluble in water. Preferably, bysoluble we mean at least 5% by weight, more preferably at least 10% byweight and especially at least 20% by weight soluble in water. Formeasuring solubility the preferred temperature of the water is 25° C.Any ionic groups are preferably neutralised to 100% as mentioned above.In the case of anionic groups the preferred neutralising agent ispotassium hydroxide, in the case of cationic groups the preferredneutralising agent is nitric acid. To properly dissolve the dispersantsof the present invention heat may be required as the dissolution processcan be kinetically very slow. Thus, a preferred method for testing thesolubility is to first heat a mixture of the dispersant, water and anyneutralising agent if needed to 80° C. for 2 hours and then to cool themixture to 25° C. and assess the solubility after a period of 24 hoursat 25° C.

Preparation of the Polymeric Dispersant

The polymeric dispersants may be made by any suitable means. Examples ofsuitable polymerisation approaches include cationic, anionic, grouptransfer and free radical polymerisation.

A preferred method is free radical polymerisation. Suitable free radicalpolymerisation methods include suspension, emulsion, bulk and preferablysolution polymerisation.

Preferably, the dispersant is prepared by the solution polymerisation ofthe above monomer composition in the presence of an aqueous or organicliquid carrier. Suitable organic liquid carriers include alcohols,ketones, ethers, amides and glycols.

Suitable free radical initiators include azos and peroxides.

The polymerisation is preferably performed with one or more chaintransfer agents. These help in achieving the preferred low molecularweights. Preferred chain transfer agents are thiols.

Dispersion

According to a second aspect of the present invention there is provideda dispersion comprising a particulate solid, a liquid medium and apolymeric dispersant according to the first aspect of the presentinvention.

The particulate solid in the dispersion preferably has a Z-averagedparticle size of from 30 to 300 nm, more preferably from 50 to 200 nm,especially from 60 to 150 nm and most especially from 70 to 120 nm. Theparticle size is preferably measured by a light scattering deviceespecially a Malvern Zetasizer™.

Preferably, the dispersion comprises:

i) 0.1 to 40 parts, more preferably 0.1 to 20 parts of the polymericdispersant;ii) 0.1 to 40 parts, more preferably 0.1 to 20 parts of the particulatesolid;iii) 50 to 99.8, more preferably 60 to 99.8 parts of the liquid medium;wherein the sum of the parts i) to iii) is 100 parts and all parts areby weight.

Preferably, the polymeric dispersant is at least partially adsorbed ontothe surface of the particulate solid. In this way the polymericdispersant best acts so as to colloidally stabilise the particulatesolid.

The amount of polymeric dispersant in the dispersion (or ink) ispreferably from 1 to 150%, more preferably from 1 to 70%, especiallyfrom 5 to 70% and more especially from 10 to 60% by weight based on theweight of particulate solid.

In a further aspect of the present invention there is provided a processfor preparing a dispersion according to the second aspect of the presentinvention which comprises dispersing, especially comminuting, acomposition comprising the polymeric dispersant according to the firstaspect of the present invention, a particulate solid and a liquidmedium. Dispersion processes include stirring, blending, shaking as wellas milling and ultrasonication, etc.

By the word comminute we mean only those processes which tend tosignificantly reduce the particle size of the particulate solid.Comminution includes for example ultrasonication, bead milling,microfluidizing and high pressure homogenising. Comminution does notinclude low shear dispersion processes such as stirring, shaking,tumbling and the like.

Further dispersants other than those according to the first aspect ofthe present invention may also be present during the preparation of thedispersion. If such further dispersant are present during thepreparation of the dispersion they are preferably present in less than50%, more preferably less than 25%, especially less than 10% and mostespecially less than 5% by weight relative to all the dispersantpresent.

Preferably, the polymer according to the first aspect of the presentinvention is the only dispersant present during the dispersion orcomminution step.

Particulate Solid

The particulate solid may be of any kind. Preferably the particulatesolid is a colorant, especially a pigment. The pigment may comprise andpreferably is an inorganic or organic pigment material or mixturethereof which is insoluble in the liquid medium. By insoluble we meanhaving a solubility of no more than 1%, more preferably no more than0.1% by weight in the liquid medium. The solubility is preferablymeasured at a temperature of 25° C. The solubility is preferablymeasured at a pH of 8. Preferably, the solubility is measured in water,more preferably deionized water.

The pigment may be organic or inorganic.

Preferred pigments include, for example any of the classes of pigmentsdescribed in the Third Edition of the Colour Index (1971) and subsequentrevisions of, and supplements thereto, under the chapter headed“Pigments”.

Examples of organic pigments are those from the azo (including disazoand condensed azo), thioindigo, indanthrone, isoindanthrone,anthanthrone, anthraquinone, isodibenzanthrone, triphendioxazine,quinacridone and phthalocyanine series, especially copper phthalocyanineand its nuclear halogenated derivatives, and also lakes of acid, basicand mordant dyes. Preferred organic pigments are phthalocyanines,especially copper phthalocyanine pigments, azo pigments, indanthrones,anthanthrones, and quinacridones.

Preferred inorganic pigments include carbon black (especially gasblacks), titanium dioxide, silicon dioxide, aluminium oxide, iron oxidesand sulfides.

For ink jet especially suitable pigments are carbon blacks, C.I. PigmentRed 122, C.I. Pigment Blue 15:3 and C.I. Pigment Yellow 74 or 155. Ofcourse there are many alternative pigments.

The pigment is preferably not surface treated so as to covalently bindwater-dispersing groups onto its surface. Preferably, the pigment is notdispersible in water without the aid of a dispersant.

We have found that the dispersants according to the first aspect of thepresent invention are especially useful for dispersing C.I. PigmentsYellows.

Examples of suitable C. I. Pigment Yellows include 1, 2, 3, 5, 6, 10,12, 13, 14, 16, 17, 62, 65, 73, 74, 75, 81, 83, 87, 90, 93, 94, 95, 97,98, 99, 100, 101, 104, 106, 108, 109, 110, 111, 113, 114, 116, 117, 120,121, 123, 124, 126, 127, 128, 129, 130, 133, 136, 138, 139, 147, 148,150, 151, 152, 153, 154, 155, 165, 166, 167, 168, 169, 170, 171, 172,173, 174, 175, 176, 177, 179, 180, 181, 182, 183, 184, 185, 187, 188,190, 191, 192, 193, 194. These can be used alone or in combination.

Of these organic azo pigments are especially preferred.

Particularly preferred C.I. Pigment Yellows include Yellow 155 andespecially Yellow 74. In our studies we have seen that C.I. PigmentYellows and C.I. Pigment Yellow 155 and 74 in particular are difficultto disperse to a suitable particle size and with sufficient colloidalstability.

Liquid Medium

For clarification the term liquid medium is used to generically describethe liquid components of the dispersion, the preferences stated forliquid media are especially targeted at dispersions which are inkprecursors or pigment concentrates. That is to say dispersions which aresuitable for storage and transport and which a customer may use to laterprepare inks and ink jet printing inks.

The liquid medium may be wholly organic but preferably is or compriseswater (i.e. is aqueous). We have found that the polymeric dispersantaccording to the first aspect of the present invention is especiallysuitable as a dispersant for aqueous liquid media.

When the dispersion is an ink precursor it is preferred that the liquidmedium is substantially aqueous. For example it is preferred that theliquid medium comprises less than 20%, more preferably less than 10%,especially less than 5% and most especially 0% of water-miscible organicliquids. Such allows the final ink formulator the best possible range ofchoices for the selection of the types and amounts of water-miscibleorganic liquids so as to best tune final ink performance to specifichardware needs.

Preferred water-miscible organic liquids for inclusion into the liquidmedium include:

-   i) C₁₋₆-alkanols, preferably methanol, ethanol, n-propanol,    isopropanol, n-butanol, sec-butanol, tert-butanol, n-pentanol,    cyclopentanol and cyclohexanol;-   ii) linear amides, preferably dimethylformamide or    dimethylacetamide;-   iii) water-miscible ethers, preferably tetrahydrofuran and dioxane;-   iv) diols, preferably diols having from 2 to 12 carbon atoms, for    example ethylene glycol, propylene glycol, butylene glycol,    pentylene glycol, hexylene glycol and thiodiglycol and oligo- and    poly-alkyleneglycols, preferably diethylene glycol, triethylene    glycol, polyethylene glycol and polypropylene glycol;-   v) triols, preferably glycerol and 1,2,6-hexanetriol;-   vi) mono-C₁₋₄-alkyl ethers of diols, preferably mono-C₁₋₄-alkyl    ethers of diols having 2 to 12 carbon atoms, especially    2-methoxyethanol, 2-(2-methoxyethoxy)ethanol,    2-(2-ethoxyethoxy)-ethanol, 2-[2-(2-methoxyethoxy) ethoxy]ethanol,    2-[2-(2-ethoxyethoxy)-ethoxy]-ethanol and ethyleneglycol    monoallylether;-   vii) cyclic amides, preferably 2-pyrrolidone,    N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, caprolactam and    1,3-dimethylimidazolidone.

Preferably, the liquid medium comprises water and optionally 1 or more,especially optionally from 1 to 3, water-miscible organic liquids.

Optional Cross-Linking

Preferably, the polymeric dispersant is cross-linked around theparticulate solid. More specifically, this equates to a dispersion ofparticulate solid particles, each particle being encapsulated with across-linked polymeric dispersant shell.

The cross-linking reaction may cross-link the polymeric dispersant byionic or more preferably by covalent bonds.

To facilitate cross-linking the polymeric dispersant may itself comprisepairs of co-reactive groups which facilitate cross-linking or thepolymeric dispersant may comprise a cross-linkable group and an externalcross-linking agent may be added.

The cross-linking reaction may utilise any of the pairs of groupsdescribed in PCT patent publication WO 2005/061087 at page 6, Table 1wherein “reactive groups in the compound” in column 2 can be read asreactive groups in a cross-linking agent.

In the case of the addition of an external cross-linking agent thepolymeric dispersant preferably has one or more cross-linkable groupsselected from hydroxy, thiol, amine, phosphonic acid and especiallycarboxylic acid acid groups.

Preferred cross-linking agents include those having isocyanate,aziridine, n-methylol, carbodiimide, oxetane, oxazoline and especiallyepoxy groups. These reactive groups are particularly useful withdispersants wherein the cross-linkable group in the polymeric dispersantis carboxylic acid groups. A preferred cross-linking agent has epoxygroups, more preferably the epoxy cross-linking agent has nocross-linking groups other than epoxy groups.

Preferred cross-linking agents include sorbitol polyglycidyl ether,glycerol polyglycidyl ether, polyglycerol polyglycidyl ether,pentaerythritol polyglycidyl ether, trimethylolpropane polyglycidylether, resorcinol diglycidyl ether, neopentyl glycol diglycidyl ether,1,6-hexanediol diglycidyl ether, hydrogenated bisphenol A diglycidylether, ethylene glycol diglycidyl ether, polyethylene glycol diglycidylether, propylene glycoldiglycidyl ether, polypropylene glycol diglycidylether, polybutadiene diglycidyl ether. Of these polyethene glycoldiglycidyl ether, trimethylolpropane polyglycidyl ether and polyglycerolpolyglycidyl ether are preferred. Cross-linking agents of this kind canbe obtained commercially under the Denacol™ tradename fromNagasechemtex.

In a preferred embodiment the cross-linking reaction is effected by anepoxy cross-linking agent and the polymeric dispersant has one or morecarboxylic acid groups.

Preferably, the cross-linking in step is performed by means of heatingthe dispersion, preferably to a temperature of from 40 to 100° C. Toaccelerate or promote the cross-linking reaction it is sometimes usefulto add a catalyst.

The pH of the dispersion whilst cross-linking is preferably from 5 to13, especially from 7 to 12.

When the cross-linking reaction involves epoxy groups it is preferredthat the reaction is performed in the presence of a borate salt and/orboric acid.

Preferably, the cross-linking step is performed by a process comprisingmixing a composition comprising the following components in thespecified proportions:

(a) 30 to 99.7 parts, preferably 50 to 97 parts, of the liquid medium;(b) 0.1 to 50 parts, preferably 1 to 30 parts, of the pigment;(c) 0.1 to 30 parts, preferably 1 to 30 parts, of the polymericdispersant; and(d) 0.001 to 30 parts, preferably 0.01 to 10 parts, of a cross-linkingagent.wherein the parts are by weight.

Preferably, the amount of cross-linking agent used in the cross-linkingreaction is stoichiometrically sufficient to reduce the acid value ofthe polymeric dispersant by 0.1 to 1.5 mmoles, more preferably from 0.1to 1 mmoles per g of polymeric dispersant. The stoichiometry calculationassumes a 100% efficient reaction between the cross-linking groups inthe cross-linking agent and the co-reactive groups in the polymericdispersant.

Optional Purification

Preferably, the dispersions are purified prior to being formulated intoan ink. The purification can be by any suitable method includingmicrofiltration, deionizer resins, centrifugation followed bydecantation and washing. A preferred method is membrane filtrationespecially ultrafiltration.

Inks

According to a third aspect of the present invention there is providedan ink comprising a dispersion according to the second aspect of thepresent invention and a liquid vehicle. Preferably, the ink is an inkjet printing ink.

By the term liquid vehicle we preferably mean the liquid components ofthe ink, where the ink is suited to printing, especially ink jetprinting.

For inks, especially an ink jet printing inks, the liquid vehiclepreferably comprises water and one or more water-miscible organicliquids as previously mentioned. The liquid vehicle may be same as thatfor the dispersions previously mentioned for the liquid medium but morecommonly the liquid vehicle for the ink comprises larger amounts of thepreviously mentioned water-miscible organic liquids.

It is preferred that the ink comprises water and less than 60% byweight, more preferably less than 50% by weight, even more preferablyless than 40%, especially less than 35% and most especially less than30% by weight of one or more water-miscible organic liquids. It ispreferred that the ink comprises at least 1%, more preferably at least5%, especially at least 10% and most especially at least 15% by weightof one or more water-miscible organic liquids.

We have found that the benefits of the improved colloidal stabilityprovided by the present polymeric dispersants are most pronounced whenthe amounts of water-miscible organic liquids is relatively high and/orwhen the water-miscible organic liquids chosen are relativelyhydrophobic.

Inks preferably comprise at least one colorant such as a dye or apigment.

Preferably, in inks the particulate solid is a pigment. Preferably, noother colorant is present in the ink.

Preferably, for ink jet printing the ink has a viscosity of less than 30mPa·s, more preferably less than 20 mPa·s and especially less than 10mPa·s. The viscosity is preferably at least 2 mPa·s. Preferably, theviscosity is Newtonian. Preferably, the viscosity is measured at 25° C.Preferably, the viscosity is measured using a shear rate of 100 s⁻¹. Theviscosity is preferably measured using a cone and plate geometry. Apreferred apparatus for measuring the viscosity is a TA Instrumentsrheometer.

Preferably, the ink comprises:

-   i) 0.1 to 10 parts, more preferably from 1 to 10 parts of polymeric    dispersant according to the first aspect of the present invention;-   ii) 0.1 to 10 parts, more preferably from 1 to 10 parts of a pigment    (acting as the particulate solid);-   iii) 80 to 99.8 parts, more preferably 80 to 98 parts of a liquid    vehicle    wherein all parts are by weight.

The ratio of polymeric dispersant to pigment is as hereinbeforepreferred.

Preferably, the ink has a surface tension of 20 to 65 dynes/cm, morepreferably 30 to 60 dynes/cm, when measured at a temperature of 25° C.The surface tension is preferably measured using a Kibron AquaPi.

The pH of the ink is preferably from 4 to 11, more preferably from 7 to10.

When the ink is to be used as ink jet printing ink, the ink preferablyhas a concentration of halide ions of less than 500 parts per million,more preferably less than 100 parts per million. It is especiallypreferred that the ink has less than 100, more preferably less than 50parts per million of divalent and trivalent metals. Parts per million asused above refers to parts by weight relative to the total weight of theink. These low concentrations of ions in the resultant ink can beachieved by the abovementioned purification step.

The ink has preferably been treated so as to remove particles having aparticle size of greater than 1 micron. This may be done bycentrifugation or filtration.

The ink may optionally contain one of more ink additives. Preferably,the ink further comprises one or more additives selected from viscositymodifiers, pH buffers, metal chelating agents, surfactants, corrosioninhibitors, biocides, dyes, water miscible organic solvent(s) and/orkogation reducing additives.

Preferably, the ink comprises a surfactant, especially a surfactantcomprising an acetylenic group. Preferred examples of which include theacetylenic diols and acetylenic ethoxylates. These can be obtained underthe tradenames Surfynol™ from Airproducts, preferred examples of whichinclude 465 and 104E.

Cartridge

According to a fourth aspect of the present invention there is providedan ink jet printer cartridge comprising a chamber which contains inkaccording to the third aspect of the present invention.

Printer

According to a fifth aspect of the present invention there is providedan in jet printer comprising a cartridge according to the fourth aspectof the present invention. The ink jet printer may be of any kind withparticular limitation including piezo, thermal, acoustic andelectrostatic ink jet printers.

Substrates

According to a sixth aspect of the present invention there is provided asubstrate printed with an ink according to the third aspect of thepresent invention.

The substrate may be of any kind without limitation. Preferredsubstrates include paper, plastic and textile materials.

Preferred substrates are papers, e.g. plain or treated papers, which mayhave an acid, alkaline or neutral character. The paper may have an inkjet receptor layer. The receptor layer may be of the swellable or porouskind. Examples of commercially available papers are as described inInternational patent application No. WO 2007/148035, page 13, line 24 tothe end of line 37, which are incorporated herein by reference thereto.Preferably, the substrate is a plain paper. Preferably, the substratedoes not contain an ink fixative. Examples of ink fixatives which arepreferably absent include cationic organic amines and cationic polymers.

Use

According to seventh aspect of the present invention there is providedthe use of a polymeric dispersant according to the first aspect of thepresent invention for preparing an ink jet printing ink.

EXAMPLES

The present invention will now be illustrated by the followingnon-limiting examples in which all parts are by weight unless indicatedto the contrary.

1. Preparation of Neutralised Polymeric Dispersant Solution—(E1) 1.1Preparation of Polymeric Dispersant Solution (DS1)

The monomers benzyl methacrylate (233.05 g, 1322.57 mmoles), propyleneglycol methacrylate (17.15 g, 118.96 mmols) and methacrylic acid (38.21g, 443.84 mmoles) were mixed together along with and a chain transferagent butyl 3-mercaptopropionate (6.80 g, 41.91 mmoles). The mixture ofmonomers and the chain transfer agent were then dissolved in diproyleneglycol (110.66 g) to give a monomer feed.

A thermal initiator, Trigonox 21S (4.80 g) was dissolved in diproyleneglycol (147.56 g) to give an initiator feed.

Dipropylene glycol (191.79 g) was warmed to 85° C. in a reaction vessel.The reaction vessel was purged by bubbling in nitrogen gas. Whilststirring the contents of the reaction vessel, the monomer and initiatorfeeds were added over 4 and 5 hours respectively. The temperature of thereactor vessel was maintained at 85° C. (+/−1° C.) throughout. The inertnitrogen gas blanket was also maintained over this period. On completionof the feeds the contents of the reactor vessel were stirred for afurther 1 hour at 85° C. These steps polymerised the monomers to preparethe polymeric dispersant (D1) in the form of a 40% by weight solution indipropylene glycol.

The molecular weight of the polymeric dispersant (D1) as measured by gelpermeation chromatography using a DMF solvent and polystyrene standardswas Mn (number average) 20,600 and Mw (weight average) 31,200. Thus,step 1 resulted in the preparation of polymeric dispersant solution(DS1).

1.2 Polymer Neutralisation

The polymeric dispersant solution (DS1) prepared above in step 1.1 (750g) was neutralised by the addition of a solution containing 45% aqueouspotassium hydroxide (44.29 g) and water (773.36 g) to give a solidscontent of 20% by weight. This prepared neutralised polymeric dispersantsolution (E1).

1.3 Preparation of Comparative Neutralised Polymeric DispersantSolutions

A series of comparative neutralised polymeric dispersant solutions CE1to CE4 were prepared exactly as in previous steps 1.1 and 1.2 exceptthat the monomer compositions indicated in Table 1 were used in place ofthose specified in step 1.1 and the amount of potassium hydroxide wasadjusted.

TABLE 1 propylene Poly Benzyl glycol propylene KOH methacrylatemethacrylate glycol methacrylic 45% Ref (BzMA) (PGMA) methacrylate acidaqu CE1 238.8 g 0 0 49.6 g 57.76 CE2 226.2 g 0 0 62.2 g 68.53 CE3 231.6g 0 19.3 g 37.6 g 43.68 CE4 211.1 g 0 40.9 g 36.4 g 42.29

Table 1, monomers compositions for comparative neutralised polymericdispersant solutions CE1 to CE4.

2. Preparation of Mill-Bases and Comparative Mill-Bases 2.1 Preparationof Mill-Base (1)

Pigment powder (22 g of TRY13—C.I. Pigment Yellow 74 pigment exDainichiSeika Color Chemicals Mfg), neutralised polymeric dispersantsolution E1 (55 g) and water (23 g) were mixed together to form apremixture.

The premixture was transferred to a horizontal recirculating bead mill(Netzsch) containing 1 mm polymeric beads and milled for 45 minutes.After the initial milling the mixture was transferred to anotherhorizontal recirculating bead mill (Netzsch) containing 0.3 mm polymericbeads. The mixture was then milled for 10 hours. The resultantdispersion was pumped off from the beads and adjusted to a solidscontent of 10% by weight of pigment by the addition of pure water. Thiswas designated Mill-base (1). The pigment particles in the resultingmill-base had a Z-average particle size of 89 nm, as measured using aMalvern Zetasizer™.

2.2 Preparation of Comparative Mill-Bases (1) to (4)

Comparative Mill-bases (1) to (4) were prepared in exactly the same wayas Mill-base (1) except that neutralised polymeric dispersant solutionsCE1 to CE4 were used in place of E1. The exact correspondence was asindicated in Table 2.

TABLE 2 Neutralised Pigment Dispersion Solution Mill-base E1 Mill-base(1) CE1 Comparative Mill-base (1) CE2 Comparative Mill-base (2) CE3Comparative Mill-base (3) CE4 Comparative Mill-base (4)

3. Preparation of Dispersions of Encapsulated Pigments 3.1 Preparationof Encapsulated Pigment Dispersion (EPD1)

The dispersant in Mill-base (1) as prepared in step 2.1 was thencross-linked using the cross-linking agent Denacol EX521 (supplied byNagase). This covalently cross-linked the carboxylic acid groups in thedispersant and thereby encapsulated the pigment particles. Thecross-linking reaction was controlled by the presence of boric acid(obtained from Aldrich). A mixture of Mill-base (1) (450 g), DenacolEX521 (0.965 g) and boric acid (0.278 g) was prepared. The cross-linkingreaction was effected by heating the above described mixture to atemperature of about 65° C. for 5 hours. This prepared encapsulatedpigment dispersion (EPD1).

3.2 Preparation of Comparative Encapsulated Pigment Dispersions CEPD1 toCEPD4

Comparative encapsulated pigment dispersions were prepared exactly asdescribed in step 3.1 except that Mill-base (1) was replaced with acomparative Mill-base. In addition, the type of cross-linking agent, theamounts of cross-linking agent and the amounts of boric acid were alsoadjusted. The exact amounts were as indicated in Table 3.

TABLE 3 Encapsulated Amount of Amount of pigment ComparativeCross-linking cross-linking Boric acid dispersion mill-base agent Typeagent (g) (g) CEPD1 CE1 EX321 0.945 0.415 CEPD2 CE2 EX321 1.575 0.695CEPD3 CE3 EX521 2.407 0.697 CEPD4 CE4 EX521 0.965 0.278

4. Ultrafiltration

Encapsulated pigment dispersions as prepared above in step 3.1 and 3.2were purified by means of ultrafiltration using a membrane having a 50kD pore size. Each encapsulated pigment dispersion was diafiltered withapproximately 10 wash volumes of pure deionized water per 1 volume ofthe encapsulated pigment dispersion. The ultrafiltration membrane wasthen used to concentrate each encapsulated dispersion back to a solidscontent of around 10% by weight.

5. Ink Preparation 5.1 Ink 1

Purified EPD 1 as prepared above in step 4 was diluted into thefollowing ink formulation to prepare Ink 1:

Ethylene glycol 15.00 g Triethylene glycol monobutyl ether 10.00 gSurfynol ™ 465  0.7 g Purified EPD 1   50 g Water  24.3 g

5.2 Comparative Inks 1 to 4

Comparative Inks 1 to 4 where prepared in the same way as Ink 1 exceptthat the purified comparative encapsulated pigment dispersions CEPD1 toCEPD4 were used.

6. Tests Methods 6.1 Average Particle Size by Light Scattering

The average particle size of the particles in each ink was measuredusing a Malvern Zetasizer™ (to record the Z-average value), and aNanotrac instrument from Microtrac Inc. (to record the My averagevalue).

6.2 Single Particle Optical Sensing (SPOS)

The number of particles having a particle size of greater than 0.5microns was measured using single particle optical sensing. Theapparatus used was an Accusizer™ 780-APS. All samples were measuredafter being diluted to 1% by weight of pigment in the ink.

The inks were stored in sealed bottles in an oven at 60° C. for 4 weeks.The inks were allowed to cool and the measurements repeated.

6.3 Sedimentation

The amount of sediment in a sample of the ink was determined visually byinspecting the bottom of a clear storage bottle for signs of sediment.The ratings were 0—none, 1—trace amounts, 2—slight amounts, 3—med and4—extensive amounts of sedimentation.

7. Testing Methodology

For each initial ink all of the tests 6.1 to 6.3 were applied. The inkswere then stored for 4 weeks at a temperature of 60° C. and the testswere repeated. The results are shown below in Table 4.

Delta Mv ave is given by Mv average after storage—Mv average initial;

Delta Z-ave is given by Z-average after storage—Z-average initial;

The SPOS result is taken from the samples after the storage test. TheRatio SPOS value is given by the SPOS value after storage divided by theinitial SPOS value.

The sediment score is taken directly from the sample after storage. Allsamples showed no sediment initially.

Results

TABLE 4 Ratio Neutralised SPOS Dispersant Delta -Mv >0.5 Sediment InkSolution ave Delta Z-ave microns score Ink 1 E1 0 0 0.79 0 ComparativeCE1 0 15 6.2 3 Ink 1 Comparative CE2 15 20 13.6 2 Ink 2 Comparative CE313 12 10.4 1 Ink 3 Comparative CE4 6 9 2.2 3 Ink 4

As can clearly be seen, Ink 1 had far better colloidal stability thanany of the Comparative Inks 1 to 4. Thus, the dispersants according tothe present invention provide dispersions and inks having excellentcolloidal stability even with difficult pigments such as C.I. PigmentYellow 74, even at higher storage temperatures of 60° C. and even ininks with more hydrophobic liquids such as triethyleneglycol monobutylether.

1. A polymeric dispersant obtained or obtainable by copolymerising amonomer composition comprising at least the components: i) benzyl(meth)acrylate; ii) propylene glycol (meth)acrylate; wherein the weightratio of component i) to component ii) is greater than 10:1.
 2. Thepolymeric dispersant according to claim 1 wherein the weight ratio ofcomponent i) to ii) is from 11:1 to 100:1.
 3. The polymeric dispersantaccording to claim 1 wherein the weight ratio of component i) to ii) isfrom 11:1 to 50:1.
 4. (canceled)
 5. The polymeric dispersant accordingto claim 1 wherein: component i) is present at from 40 to 95 parts;component ii) is present at from 0.1 to 9 parts; wherein all parts areby weight.
 6. The polymeric dispersant according to claim 1 wherein themonomer composition further comprises: iii) one or more ethylenicallyunsaturated hydrophilic monomers each having one or more ionic groups.7. The polymeric dispersant according to claim 6 wherein component iii)is or comprises methacrylic acid.
 8. The polymeric dispersant accordingto claim 1 wherein the monomer composition comprises no more than 2parts by weight of macromonomer and the sum of all the parts of themonomer components is 100 parts by weight.
 9. A dispersion comprising aparticulate solid, a liquid medium and a polymeric dispersant accordingto claim
 1. 10. The dispersion according to claim 9 wherein thepolymeric dispersant is cross-linked around the particulate solid. 11.The dispersion according to claim 22 wherein the particulate solid is apigment.
 12. (canceled)
 13. The dispersion according to claim 24 whereinthe pigment is C.I. Pigment Yellow 74 and/or C.I. Pigment Yellow 155.14. An ink comprising a dispersion according to claim 1 and a liquidvehicle.
 15. The ink according to claim 14 being an ink jet printer ink.16. An ink jet printer cartridge comprising a chamber and an ink,wherein the ink is as defined in claim 25 and the chamber contains theink.
 17. (canceled)
 18. (canceled)
 19. (canceled)
 20. (canceled)
 21. Apolymeric dispersant according to claim 1 wherein: (a) the weight ratioof component i) to ii) is from 11:1 to 50:1; (b) component i) is presentat from 40 to 95 parts; and component ii) is present at from 0.1 to 9parts; wherein all parts are by weight; (c) the monomer compositionfurther comprises: iii) one or more ethylenically unsaturatedhydrophilic monomers each having one or more ionic groups; and (d)component iii) is or comprises methacrylic acid.
 22. A dispersioncomprising a particulate solid, a liquid medium and a polymericdispersant according to claim
 21. 23. The dispersion according to claim22 wherein the polymeric dispersant is cross-linked around theparticulate solid.
 24. The dispersion according to claim 10 wherein theparticulate solid is a pigment.
 25. An ink comprising a dispersionaccording to claim 24 and a liquid vehicle.
 26. The ink of claim 25being an ink jet printer ink.